assistant: add hack to increase TTS volume

Bug: b/111601093
Test: Manual
Change-Id: I8843c9fc0654cc0db5a6209bd32bda418992bd34
Reviewed-on: https://chromium-review.googlesource.com/1161336Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Commit-Queue: Muyuan Li <muyuanli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580368}

chromeos/services/assistant/assistant_manager_service_impl.cc

@@ -57,6 +57,9 @@ AssistantManagerServiceImpl::AssistantManagerServiceImpl(
       background_thread_("background thread"),
       weak_factory_(this) {
   background_thread_.Start();
+  background_thread_.task_runner()->PostTask(
+      FROM_HERE, base::BindOnce(&AssistantManagerServiceImpl::SetVolumeHack,
+                                base::Unretained(this)));
   connector->BindInterface(ash::mojom::kServiceName,
                            &voice_interaction_controller_);
 
@@ -759,5 +762,10 @@ void AssistantManagerServiceImpl::SendContextQueryAndRunCallback(
   std::move(callback).Run();
 }
 
+void AssistantManagerServiceImpl::SetVolumeHack() {
+  DCHECK(background_thread_.task_runner()->BelongsToCurrentThread());
+  platform_api_.GetFileProvider().WriteFile("assistant/volume/system", "1.0");
+}
+
 }  // namespace assistant
 }  // namespace chromeos

chromeos/services/assistant/assistant_manager_service_impl.h

@@ -193,6 +193,10 @@ class AssistantManagerServiceImpl
   void OnAssistantScreenshotReceived(base::OnceClosure on_done,
                                      const std::vector<uint8_t>& jpg_image);
 
+  // Writes a file to assistant's path to force assistant volume to 100%.
+  // TODO(muyuanli): Remove once AudioOutputImpl is checked in.
+  void SetVolumeHack();
+
   State state_ = State::STOPPED;
   PlatformApiImpl platform_api_;
   bool enable_hotword_;